Usually, in order to transmit the image information coming from the sensor placed inside the mouth to a receiver system, a cable connection that is also used to control the sensor and supply it with energy.
The drawback of a cable connection is that it is fragile (risk of being pulled out), inconvenient for the patient if the cable is accidently pulled, and bulky in the overall installation. In addition, in the medical environment the constraints of electrical insulation between the patient and the surrounding electrical power supplies are heightened and it is hardly in accordance with these constraints to connect a mains-powered device (microcomputer) to a module that is in the patient's mouth.
It has therefore been attempted to produce wireless connections both for providing energy and for conveying the information coming from the sensor or toward the sensor. As wireless energy supply (typically by inductive transmission) is not very convenient, it is generally preferred to use a small-sized battery in the sensor placed in the mouth. Furthermore, the image information coming from the sensor must be transmitted at a high data rate (of around 20 megabits per second), and this is why radiofrequency transmissions are preferred, preferably in the unlicensed frequency bands, which are in practice those which are used for wireless communication of information in local networks (frequencies allocated to WLAN networks: 2.45 GHz for example).
However, the difficulty arises in that this radio transmission may then be strongly interfered with through the presence of other radio transmitters which are being used increasingly in IT environments; WiFi or Bluetooth peripherals and computer cards may in particular strongly interfere with the transmission of image data from the sensor to the image user system.
This difficulty can be reduced by emitting the messages in a redundant manner in order to ensure complete and reliable transmission of every image, but this is time consuming when the information to be transmitted is already of a large quantity (typically several tens of megabits per image).
It is also possible to use an “smart” transmitter which examines which frequencies are not used locally in the environment and which adapts its own frequency and/or its own data rate depending on this environment. Such a transmitter necessarily also comprises a receiver. The complex electronics for reception, analysis and intelligent processing that results from this makes it very difficult to put the assembly into the patient's mouth. The bulk and the power consumption are prohibitive. It is therefore necessary to divide the system into a sensor situated inside the mouth, a connecting cable starting from the sensor and which comes out the mouth, a transmitter-receiver in a pocket of the patient, and an intelligent radiofrequency connection between this extraoral transmitter-receiver and the user system (microcomputer) which must collect the images. Such an installation is complex.
Furthermore, in the patent application FR 2 883 719, an intraoral dental sensor is described which provides information to the user system (a personal computer for example) by wireless optical means, in the form of a modulation of the light emitted by a source. The sensor comprises a light source placed on the sensor, and therefore in the mouth, and an optical fiber connected inside the mouth to this source to receive from it light modulated by the sensor. The fiber leaves the mouth and has a free end through which it emits light and the light is received by a receiver connected to the user system. The free end of the fiber is provided with a light diffuser (a small ball of translucent material) which enables approximately omnidirectional light emission.
However, the efficiency of the light transmission toward the receiver is not optimum.